docs: def lock_reward(self, agreement_id, amount, account):
          """
          Lock reward condition.
  
          :param agreement_id: id of the agreement, hex str
          :param amount: Amount of tokens, int
          :param account: Account
          :return: bool
          """
          return self._keeper.lock_reward_condition.fulfill(
              agreement_id, self._keeper.escrow_reward_condition.address, amount, account
          )